Hydraulic brake system with slip control

ABSTRACT

The present invention relates to a brake system with slip control, including digitally operated electromagnetic inlet and outlet valves, wherein the inlet valve is provided with a restrictor valve control responsive to differential pressures. To prevent a premature operation of the controllable restrictor, invariable orifices are arranged in the main pressure line upstream of the inlet valve and downstream of the controllable restrictor.

TECHNICAL FIELD

The present invention relates to vehicle brake systems and moreparticularly relates to hydraulic brake system with slip control.

BACKGROUND OF THE INVENTION

Discontinuous fluid pressure associated with digitally controlled causesundesirable noise emission due to the pulse-like pressure variation anddue to the noise emanating from the inlet and outlet valves associatedwith the digital control of the fluid.

As disclosed in patent application Ser. No. DE 43 19 227.0, digitallycontrolled brake systems are generally known. However, it has been foundin the brake system described in application number 43 19 227.0 that, onquick operation of the brake (emergency braking), an undesirablepremature activation of the restrictor, connected downstream of theinlet valve, cannot be prevented with sufficient reliablity. Such apremature restrictor activation causes change of the pedal feeling andthe vehicle-related gradient of pressure increase. More particularly,the reduction of the pressure-increase gradient caused by the restrictoreffect reduces the braking efficiency in slip-free, dynamically stabledriving operations.

European patent application 0 317 305 discloses a solenoid valve whichis suitable for use in anti-lock hydraulic brake systems. The solenoidvalve has a magnetic core accommodating a coil. The magnetic core isconfined by a magnetic armature on one side and by a restrictor memberon the other side. The restrictor member has a passage which is closableby a valve needle. The restrictor member is compressed in an axiallymovable fashion between the magnetic core and a housing cover in whichthe pressure fluid inlet is provided, so that in the operatingcondition, where the valve needle closes off the supply duct in therestrictor member, a differential pressure acts on either side of therestrictor member and causes displacement of the valve needle inrelation to the magnetic armature. This preloads a compression springinterposed between the valve needle and the magnetic armature. Thepreloading force of the compression spring produced by the difference inpressure on the restrictor member causes a quick release of the magneticarmature from the magnetic core when the electromagnetic excitation isinterrupted. This results in short valve opening times. A springresetting force acting on the valve needle in the opening sense favorsthe quick opening of the supply duct in the restrictor member. Thus,pressure fluid propagates to an annular slot after having passed throughthe free passage at the valve needle. The annular slot is providedbetween the hollow-cylindrical inside wall of the magnetic core and theoutside wall of a cylindrical part in which the valve needle extends.The fluid which emanates from the valve inlet is conducted through thesupply duct in the restrictor member and the subsequent annular slotinto a pressure fluid connection which leads to the pressure fluidconsumer.

Therefore, an object of the present invention is to maintain a virtuallymodified simple structure of the brake system which resulted from themain application, and to provide a solution with respect to preventing apremature undesirable activation of the controllable restrictor.

SUMMARY OF THE INVENTION

This object is achieved, according to the present invention, whereininvariable orifices are arranged in the main pressure line upstream ofthe inlet valve and downstream of the controllable restrictor.

Thus, favorably, the pressure increase speed in the control pressureport activating the restrictor valve is limited by way of the invariableorifice connected upstream of the inlet valve in the phase of pressureincrease which is caused by operation of the master cylinder. Anotherinvariable orifice, which is connected downstream of the controllablerestrictor, supports the inactive condition of the controllablerestrictor by a correspondingly raised pressure increase speed inanother control pressure port of the restrictor valve, so that thecontrollable restrictor is ineffective in the slip-free normal brakingmode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hydraulic circuit of the brake system according to thepresent invention.

FIG. 2 is a partial cross-sectional view of an inlet valve of the brakesystem according to the present invention.

FIG. 3 is another partial view of an alternative embodiment of the inletvalve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic view of the hydraulic circuit for the brake systemof the present invention. A braking pressure generator 5 is connected toa wheel brake 3 by way of a main pressure line 2. An inlet valve 1,which is electromagnetically open in the basic condition, and arestrictor 4, which is connected downstream of the inlet valve 1 and isinoperative in the basic condition, are comprised in the main pressureline 2. The controllable restrictor 4 is represented as atwo-way/two-position directional control valve. A first control pressureport 6 is acted upon by the pressure of the braking pressure generator 5and the pump pressure. A second, counteracting control pressure port 6'of the two-way/two-position directional control valve is acted upon bythe pressure in the wheel brake 3. A compression spring 7, shownsymbolically on the 2/2-way valve, ensures that the pressure fluid flowto the wheel brake 3 is initially unthrottled. In addition, a returnline 16 is connected to the wheel brake 3 and is connected to thesuction side of an auxiliary-pressure pump 18 by way of anelectromagnetic outlet valve 17 which is closed in its basic condition.Further, the return line 16 has a low-pressure accumulator 19 for theintermediate storage of excessive pressure fluid volume. The pressureside of the auxiliary-pressure pump 18 is connected to the brakingpressure generator 5 by way of an auxiliary-pressure line 20 and, inturn, to the main pressure line 2. An invariable orifice 26 is arrangedbetween the connection of the auxiliary pressure line 20 and the inletvalve 1 to the main pressure line 2. Another invariable orifice 27 ispositioned between the controllable restrictor 4 and the connection ofthe outlet valve 17 to the main pressure line 2 upstream of the wheelbrake 3. The invariable orifice 26 connected upstream of the controlpressure port 6 will always maintain the desired pressure increasegradient in the hydraulic system connected downstream of the invariableorifice, so that pressure peaks of an emergency braking will not causeundesirable operation of the restrictor 4 in the normal braking mode.

The restrictor valve configuration according to the present inventionpermits reducing the valve operating noises in the inlet valve 1 duringslip control and, thus, during operation of the pump 18 as soon as, inthe closed condition of the inlet valve, pressure in front of the inletvalve 1, which rises in a calibrated manner due to the invariableorifice 26, causes an increased difference in pressure, compared to thewheel braking pressure, which controls the activation of the restrictor4 accordingly. The invariable orifice 27, which is connected downstreamof the controllable restrictor 4, is interposed between the furthercontrol pressure port 6' and the connection of the return line 16 to themain pressure line 2, so that a predetermined pressure increase gradientis also achieved at the further control pressure port 6' during brakeoperation and determines the operating point of the restrictor 4. Therapid pressure reduction in the wheel brake 3 is not impaired by theeffect of the invariable orifice because the wheel braking pressure isnot impeded to escape either through a non-return valve 29 or, duringslip control, through the open outlet valve 17.

FIG. 2 shows a constructive embodiment of the arrangement of theinvariable orifice 27 in a valve-accommodating member 9 and the designof the inlet valve 1. The inlet valve 1 has a valve carrier 10 includingvalve closure member 11 and the ducting of the main pressure line 2.Favorably, the valve carrier 10 is integrated in the valve-accommodatingmember 9 in a cartridge-type construction (screw-in cartridge). Pressurefluid in the main pressure line 2 propagates from the braking pressuregenerator 5 (symbolically shown) through the invariable orifice 26(which is not explicitly shown in the valve-accommodating member) andthrough a plate-type filter 21, the open valve closure member, anannular filter element 22 inserted in the valve carrier 10 to atransverse bore 13 which is partially overlapping with the annularpiston 8 in the present Figure. Due to its restrictor 4 arranged at thefrontal end, the annular piston 8 performs the restrictor function and,accordingly, varies the stroke of the annular piston 8 and, thus, theflow cross-section between the transverse bore 13 and the end surface ofthe annular piston as a function of the differential pressure. Theannular piston 8 is radially guided on the extension of the valvecarrier 10 and, by the action of a compression spring 7, is supported ona bead acting as a stop between the stepped bore of thevalve-accommodating member 9 and the extension. The plate-type filter 21is attached by way of a retaining bowl staked on the extension. Thecompression spring 7 is compressed as a helical spring between theenlarged end surface portion of the valve carrier 10 and the adjacentend surface of the annular piston 8 in a manner which optimizes mountingspace requirements. It should be mentioned that parts of the valvecarrier 10, such as the extension or the valve seat accommodating thevalve closure member 11, can include the invariable orifice 26.

With increasing hydraulic differential pressure on either side of theannular piston end surfaces and, thus, within the hydraulic line 2 infront of and behind the inlet valve 1, the annular piston 8 is displacedupwardly in opposition to the compression spring 7. Thereby, the annularpiston will overlap the transverse bore 13 and reduce the flowcross-section to the size of the restrictor bore. To pressurize thesmall annular end surface on the annular piston 8 which is remote fromthe compression spring 7, a corresponding space is provided between theperipheral surface oft he plate-type filter 21 and the peripheralsurface of a guide ring 30. The space serves to operate an O-ring 24 andthe bottom part of the annular piston 8 hydraulically. When dimensionedaccordingly, the space can also perform the function of the invariableorifice 26.

Also, the plate-type filter 21, as a plastic part, can be placed ontothe periphery of the valve carrier 10. To improve the valve assembly,the small-clearance guide ring 30 and the O-ring 24 are placed on top ofthis arrangement so that the pressure-relief function is performed byway of a spherical non-return valve 23 which is arranged separately inthe valve carrier 10. Thus, the O-ring 24 is exclusively intended toseal the annular piston 8. It is also possible to replace the sphericalnon-return valve 23 and to use an annular sleeve at the location of theO-ring 24.

As an example, a screw-type thread is used to attach the valve. Furthertypes of attachment by calking or form-lock connections by a circlip arepossible.

In contrast to the preceding embodiment of FIG. 2, FIG. 3 shows anotheralternative construction of inlet valve 1 to achieve the controllablerestrictor function in coaction with the preceding invariable orificearrangement by way of a control piston 14, which is structurallyarranged in parallel to the valve closure member 11. Control piston 14is guided radially in the valve carrier 10, sealed at the piston stem byO-ring 24, and it is supported with its end surface on a stop disc 25snapped into the valve carrier 10. The opposite end surface of thecontrol piston 14 is acted upon by a compression spring 7 as in thepreceding embodiments. The aperture of the control piston 14 has ablind-end bore and, vertically to this bore, a restrictor 4 terminatingin the bore. Corresponding to its shape, the restrictor has arestricting flow cross-section within the transverse bore 13, associatedwith, the main pressure line 2, so that the control piston 14 will shutoff the transverse bore 13, except for the restricting cross-section,with an increasing pressure difference between the braking pressuregenerator 5 and the wheel brake 3. The transverse bore 13 of the valvecarrier accommodates the invariable orifice 27. A feature of thedescribed embodiment is the low-cost manufacture of the control piston14 and the associated accommodating bore 15. The valve carrier 10 isretained in the valve-accommodating member 9 by self-calking in theembodiment shown. However, attachment of the valve is also possible byusing other variants of force-locking and/or form-locking connectingmethods, without the need for detailed explanations.

Similar to the invariable orifice 27 on the wheel brake side, thefurther invariable orifice 26 provided at the connection of theauxiliary pressure line 20 to the main pressure line 2 is favorablyarranged in the valve carrier 10 and, thus, below the control piston 14.If ducting allows it, the invariable orifice 26 can also be arranged inthe valve-accommodating member 9.

The embodiments referred to hereinabove permit a particularly compactintegration of controllable restrictors and invariable orifices in thevalve carrier 10 or the valve-accommodating member 9, without requiringintricate modifications to the valve construction. In contrast to FIG.2, the non-return valve 23 is arranged in the valve carrier 10 and isconnected to the main pressure line 2 (annular chamber) connected to thewheel brake 3 by way of a channel in the valve carrier 10.

Of course, the suggested embodiments with respect to the inlet valve canbe used irrespective of the arrangement of invariable orifices 26, 27 inthe hydraulic circuit, which was described in FIG. 1. Therefore, theinlet valve constructions can be considered as favorable detailsregardless of the approach to the present invention.

We claim:
 1. A hydraulic brake system with slip control, of the typeincluding a braking pressure generator which is hydraulically connectedto at least one wheel brake by way of a main pressure line, a returnline connected to the wheel brake and to a pressure-fluid collectingmeans, an auxiliary-pressure pump having an auxiliary-pressure line andbeing hydraulically connected to the braking pressure generator, andinlet and outlet valves inserted into the main pressure line and thereturn line and either closing or keeping open the pressure fluidpassage in the main pressure line and in the return line, a controllablerestrictor arranged in the main pressure line between the inlet valveand the wheel brake, permitting an unhindered hydraulic fluid flow inthe main pressure line to the wheel brake in a first operating positionand limiting the pressure fluid flow to the wheel brake in a secondoperating position, comprising:a first invariable orifice arranged inthe main pressure line upstream of the inlet valve and a secondinvariable orifice arranged downstream of the controllable restrictor.2. A hydraulic brake system as claimed in claim 1 wherein the firstinvariable orifice preceding the inlet valve is arranged between theconnection of the auxiliary-pressure line to the main pressure line anda first control pressure port associated with the controllablerestrictor, wherein the invariable orifice, serially arranged downstreamof the controllable restrictor, is inserted between the connection ofthe return line to the main pressure line and a second control pressureport associated with the restrictor.
 3. A hydraulic brake system asclaimed in claim 2 wherein said first control pressure port ispositioned between the first invariable orifice and the inlet valve,wherein the second control pressure port, which provides the unimpededopen basic condition of the controllable restrictor, is positionedbetween the second invariable orifice and the controllable restrictor.4. A hydraulic brake system as claimed in claim 1, further including aby-pass line, which includes a non-return valve that opens in thedirection of the braking pressure generator, connected to the mainpressure line upstream of the first invariable orifice and downstream ofthe second invariable orifice.
 5. A hydraulic brake system as claimed inclaim 1, wherein the invariable orifices are an integral part of avalve-accommodating member which accommodates the inlet valve and thecontrollable restrictor.